As @joshua_horton noted, in Keyman 15, we made the decision to support only one, hardcoded double-tap gesture on Shift to move to the caps layer, which covers the majority of keyboards that need this functionality. This was intended as a stop-gap until we completed generic multi-tap gesture support, at which point you’d be able to define your own double-tap on Shift to move to any layer you desire. There were two aspects to this:
- Support for defining multi-tap gestures in the .keyman-touch-layout file, now supported in Keyman 16 beta
- Generalized support for multi-tap in Keyman Engine for Web, still in development
It would (in theory at least) be possible to improve our stop-gap measure for the Shift key to allow a double-tap to target an alternate layer, by making use of those additional multi-tap gestures bdefined in the .keyman-touch-layout file now. That change would meet your need for now but would be a dead-end change in that we’d be rolling it back out for full multi-tap gesture support. It would be a very constrained patch with caveats – it would only support layer switching with the nextlayer control, and not character output, so I am somewhat hesitant. But as far as I can tell, such a tweak would be forward-compatible with the format changes.
What do you think @joshua_horton? We’d be building this tweak with the plan to back it out with proper gesture support, so we’d only be reading the additional multi-tap data from the touch layout in order to get a different target layer name. The changes should be limited to pendingMultiTap.ts.